A type of membrane pump known for a long time has a pump head provided with a recess. See, for example, the German Offenlegungsschrift 1 184 447. The pumping chamber is located in the recess and, on the side of the pump drive, is closed by a flat membrane, e.g., a disc-like membrane. The pumping action is achieved by moving the membrane via a rod. The rod has a free end, and sections of the membrane are alternately gripped and stretched by the free end of the rod and an associated fastening disc. The other end of the rod is mounted eccentrically on a crankshaft so that, during operation of the pump, a lifting movement occurs approximately perpendicular to the plane of the flat membrane.
Such a membrane pump has the advantage, among others, that no lubricant and lubricant vapors enter the pumping chamber. On the other hand, a drawback of this membrane pump, among others, is its relatively noisy operation due to the back-and-forth motion of the rod and membrane.
Also known is a membrane pump having an annular pumping chamber which is bounded radially by a solid outer wall and an inner wall constituted by a deformable, annular membrane. See, for instance, the German patent 2 911 609. The annular membrane is moved by a circumferentially travelling drum. In this type of membrane pump, the inlet and outlet may be located next to one another and the pumping chamber divided by a clamped section of the membrane disposed between the inlet and the outlet.
The annular membrane and associated pump are expensive to manufacture and still require a crank drive. The travelling drum prevents simple design and manufacture of the membrane which constitutes a wear component of the pump. Moreover, replacement of the annular membrane is relatively difficult. In addition, the annular membrane requires a relatively large amount of space.